USGS has produced topographic maps of American landscapes for more than a century as part of its Congressional mandate to maintain the elevation data that helps document change across the Nation. The use of LiDAR, refined at EROS, is key to modern topography.
EROS Plays Major Role in Evolution of Lidar Technology and Applications
At 186,000 miles per second, speeding pulses of light can reveal a lot about Earth’s landscapes.
Like where previously undetected fault lines exist. Where ground surface is swelling and sinking around a bubbling volcanic cauldron. Where ancient burial mounds lay hidden deep beneath forest canopies.
The remote-sensing technology enabling all this is called lidar, short for Light Detection and Ranging. Lidar systems fire light waves from a laser mounted on an aircraft to measure ranges—or variable distances—to the Earth. Combined with other Global Positioning System (GPS) and inertial position data recorded by the airborne system, these light pulses generate precise, three-dimensional Point Cloud information about the shape of the planet and its surface characteristics.
That kind of information is valuable to government and private organizations working on flood risk management, infrastructure construction, energy development, and more. It’s particularly pertinent to the USGS, which has produced topographic maps of American landscapes for more than a century as part of its Congressional mandate to maintain the elevation data that helps document change across the Nation.
A Paradigm Shift
Lidar has become such a paradigm shift in accurately measuring terrestrial elevations that an effort called the 3D Elevation Program (3DEP) was formed in the last five years to bring that enhanced elevation data to the needs of 34 Federal agencies, all 50 states, tribal and local governments, and the private sector. Led by the USGS National Geospatial Program—and relying heavily on lidar expertise at the Earth Resources Observation and Science (EROS) Center—3DEP has been so successful in such a short time that USGS earned the “Outstanding Enterprise Achievement in LiDAR” award in February 2018 at the International LiDAR Mapping Forum in Denver, CO.
Staff at the EROS Center played no small role in that success, said Greg Stensaas, who manages the Requirements, Capabilities, and Analysis for Earth Observation (RCA-EO) project at EROS. The original USGS Elevation and Lidar Point Cloud process was established at EROS. The Elevation team at the Center started doing lidar work in 2002, and the Center for LIDAR Information Coordination & Knowledge (CLICK) came into being at EROS in 2006.
“The important part (in the award recognition) is standing up something of national significance and value for all Federal agencies in such a short time,” Stensaas said. “Establishing new quality mechanisms and processes to ensure that we get the data we need to do the science applications accurately is a huge accomplishment. EROS was right in the middle of supporting data quality and specifications.”
The award recognizes the tremendous work 3DEP has done to build lidar acquisition partnerships among various governmental and private entities, with a goal of accomplishing nationwide lidar coverage within eight years. But the program is involved in much more than just gathering data. The 3DEP team has spent considerable time promoting its use, as well as advancements in lidar technology. The program has worked hard to make the data visible and freely accessible, while working to improve the data acquisition and data quality.
EROS Influences 3DEP Research
EROS’ influence has really come in the research arm of 3DEP, Stensaas said. Center staff are tasked with making sure the quality of lidar data is well understood. They also are ensuring that there is good reference information for Point Clouds—3D visualizations processed from measurements acquired as millions of light pulses are fired at an object or surface below and then reflected back to an airborne scanner. Elevations for the ground, buildings, forest canopy, highway overpasses, and anything else that the laser beams encounter during a survey can make up Point Cloud data.
One of the recent significant contributions from the EROS Point Cloud Group—comprised of Stensaas, Jeff Danielson, Dean Gesch, Karl Heidemann, Jeff Irwin, Sandra Poppenga, Ajit Sampth, and Minsu Kim—is the establishment of an interswath data quality measurement process for 3DEP including the development of associated software and processes for Point Cloud geometric data quality. This group was also instrumental in documenting what needs to be done in the lidar community to make the data better, well understood, and usable. Both of these areas are now documented and available community-wide in ASPRS Guidelines.
“That whole effort of establishing the quality processes for the 3DEP is the forte of work we’re doing at EROS,” Stensaas said. “Of course, we have a lot more yet to do.”
One 3DEP vision for the future is a National Terrain Model that merges topography maps with bathymetry data, or underwater land surface and water depth. Measuring sub-surface elevations in rivers and lakes is important for such things as navigational safety. Work in that area is a natural fit for EROS staff who are already a major player in Coastal National Elevation (CoNED) work, which looks at coastal shoreline elevations, as well in Digital Elevation Models (DEM).
Danielson, a physical geographer at EROS, said the green, water-penetrating wavelengths on lidar are particularly useful in looking at edges and slopes around inland and coastal water bodies and accurately estimating terrestrial elevations beneath the water surface.
“We’re doing that kind of work right now,” Danielson said. “We’re not doing the actual hydrology applications, but we’re doing the validation of these green laser systems on the Kootenai River, looking at the quality of the data and the performance of the sensor.”
Using Lidar to Map Rivers, Lakes
This research will help 3DEP work toward operationalizing topobathymetric lidar by providing recommendations regarding topobathy lidar sensor performance and suitable site conditions for potential river acquisition surveys, Danielson said.
Currently, 3DEP provides 1-meter DEMs that depict the surface of lakes and reservoirs as flat, and rivers that are flat from shore to shore. But the opportunity for enhancing that with inland bathymetry is as realistic as any number of advanced 3DEP products that are more than just DEMs, Danielson said, whether it involves canopy cover or biomass or mapping infrastructure.
“The vision is eventually to go into the ‘Cloud,’ and have the Lidar Point Cloud sitting in the Cloud next to numerous other remote-sensing datasets,” Danielson said. “Then people just basically bring their algorithms and crank out on-demand products that are more than just a DEM.”
In a way, Stensaas likens it to efforts going on now with Landsat images and the evolution of analysis ready data. “The goal would be for the whole Point Cloud to be available for any kind of widgets, applications, and algorithms that people want to use,” he said.
That day is coming. 3DEP is not at national coverage yet; it’s still developing. But the potential of lidar is unmistakable, Danielson and Stensaas say, and EROS is playing a major role in helping to bring those possibilities to reality.
“We have good folks here at EROS who are probably some of the best lidar experts in the community,” Stensaas said. “We have people here who are experts on the terrain elevation modeling. We have people who are experts on lidar modeling and biomass. We have people who are experts with its use in hydrology and bathymetry. These are all important research areas for the use of lidar. That use of lidar information is growing rapidly, and these lidar use areas will continue to expand in the future.”
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